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problem using floor function

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Join Date: Sep 2009

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I_Empire

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problem using floor function

Oct 16th, 2009

i am writing a function to convert fractions to intgers for example:
.636 -> 636 or .45 -> 45

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 C++ Syntax (Toggle Plain Text) 
int ret_int(double input)
{
	while(true)
	{
                // this line is for debugging only
	cout  << input << "  "  << floor(input) << endl;
 
	if(input == floor(input)) return input;
	input = input * 10;
	}
}
int ret_int(double input)
{
	while(true)
	{
                // this line is for debugging only
	cout  << input << "  "  << floor(input) << endl;

	if(input == floor(input)) return input;
	input = input * 10;
	}
}

for some inputs it is working fine for example:

Click image for larger version

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Views: 8
Size: 20.4 KB
ID: 12148

But for some inputs :

Click image for larger version

Name: 2.jpg
Views: 8
Size: 29.6 KB
ID: 12149

which i cant understand the floor and the input are the same so why the function does not return

some inputs also do this:

Click image for larger version

Name: 3.jpg
Views: 7
Size: 25.5 KB
ID: 12150

floor(23450) = 23499

weird?
if anybody has another approach (another method) to do the job i would be thankful

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Join Date: Jul 2009

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ryuslash

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-1

Oct 16th, 2009

I had very similar output in one of my project, it seems I declared a double somewhere, but didn't instantiate it...

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cpp Syntax (Toggle Plain Text)

double somedouble;

I don't know if this is applicable to you, but now that I've instantiated it, it seems to be better...

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cpp Syntax (Toggle Plain Text)

double somedouble = 0.0;

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Join Date: Sep 2009

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I_Empire

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Oct 16th, 2009

No there is nothing to initialize
and even if why?

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Join Date: Oct 2009

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Zjarek

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Oct 16th, 2009

Remember: 2.0+2.0!=4.0. I think this is just roundoff error, .245*1000 can be smaller then 245.
edit: Solution: define new class for double and make new operator== which will do something like that:

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if(a<b*(1+epsilon) && a>b*(1-epsilon)) return true;
return fals;
if(a<b*(1+epsilon) && a>b*(1-epsilon)) return true;
return fals;

where epsilon is desired precision (10**-10 would be good).

Last edited by Zjarek; Oct 16th, 2009 at 6:53 pm.

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Join Date: Sep 2009

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I_Empire

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Oct 17th, 2009

constructing a whole class to solve such a problem!
is nt there any simpler solutions

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tux4life

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Oct 17th, 2009

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Originally Posted by I_Empire

constructing a whole class to solve such a problem!
is nt there any simpler solutions

http://www.parashift.com/c++-faq-lit...html#faq-29.17

"Never argue with idiots, they just drag you down to their level and then beat you with experience."

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Join Date: Sep 2009

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I_Empire

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Oct 23rd, 2009

ok i did what the website told me to do , writing a function to check if two double numbers are equal or not , this solved the first problem when the input is .23 for eample (see the second picture in my first post)

but it did not solve the second problem (see the third picture in my first post) : floor(2345) = 2344

this is a problem with the floor function .

any suggestions !